Composite materials are packaging materials composed of at least two different materials bonded to one another over an entire area and not amenable to manual separation. They are a subgroup of the layer laminates and therefore of the laminates in general. Packaging produced therefrom is called composite-material packaging or composite packaging.
The drinks carton is typical composite packaging. It is composed of paper board and of polyethylene plastic, and for products with long shelf lives, such as juices, it can also comprise a layer of aluminum. Butter wrapping (aluminum/paper), plastics-coated cartons for deep-frozen foods, and pouches for instant soups (aluminum/plastic) are other commonly used types of packaging made of composite materials.
Restriction of contact between oxygen and oxygen-sensitive products conserves and improves the quality of many products and the storage times of the same. By way of example, restriction of contact between oxygen and oxygen-sensitive food products in a packaging system can conserve the quality of the food product and delay spoiling. This type of packaging also increases the time for which the product can be kept in stock, thus reducing the costs incurred through waste and restocking.
The food-and-drink industry has developed some techniques for restricting contact with oxygen. Conventional techniques include those where certain means which differ from the packaged item and from the packaging material are used to consume oxygen within the environment of the packaging (an example being use of small pouches of oxygen-scavenging material), those which create reduced-oxygen-content environments within the packaging (examples being packing under modified atmosphere and vacuum packing), and those that prevent ingress of oxygen into the packaging environment (examples being barrier films). Combinations of the techniques mentioned are moreover very frequently used. In the case of the barrier films, a distinction has to be made between films composed of an oxygen-impermeable material (passive barrier property) and films comprising a material which binds the oxygen chemically or physically (active barrier properties). Systems with combined active and passive barrier action, with single- and multilayer structures, are frequently used.
By way of example, oxygen-scavenging materials have been incorporated directly into the structure of the packaging. This technique (hereinafter termed “active oxygen barrier”) can provide a uniform scavenging effect within the entire packaging, and a means of intercepting and trapping oxygen that passes through the walls of the packaging. Active oxygen barriers have been formed through incorporation of inorganic powders and/or salts as part of the packaging, and described by way of example in U.S. Pat. Nos. 5,153,038, 5,116,660, 5,143,769 or 5,089,323. However, the incorporation of powders and/or salts of this type can impair the transparency and the mechanical properties of the packaging material, and can complicate processing, in particular where thin films are required. Furthermore, these compounds, and oxidation products thereof, can be absorbed by the food in the container, and within the food product this can lead to non-compliance with national standards for human consumption.
Oxygen-scavenging compositions comprising transition metal catalysts and ethylenically unsaturated hydrocarbon polymers are disclosed in U.S. Pat. No. 5,399,289. The polymers described in that document are amorphous, and they can therefore be difficult to mix and to process with film-forming semicrystalline polymers which are conventionally used to provide flexibility to packaging materials.
WO 1998012244A1 describes, for use as oxygen-removing materials, polycondensation copolymers composed mainly of polyester segments and of polyolefin segments based on 1,3 butadiene. However, the incorporation of the oxygen-scavenging polybutadiene segments here is restricted to a PET matrix, and cannot be extended to other polymer matrices.
A polymeric material for use in an oxygen-scavenging composition should ideally exhibit good processing properties, be amenable to direct formation within the ready-to-use packaging materials, or have high compatibility with the polymers that are usually used to produce packaging materials. The appropriate materials should moreover produce no by-products that impair the color, taste or odor of the packaged product. Migration of monomers or oligomers from the single—or multilayer film into the interior of the packaging container should therefore as far as possible be prevented. A packaging material formed from a composition of this type is ideally capable of retaining its physical properties after scavenging a suitable quantity of oxygen.
The present invention achieves the abovementioned complex technical object. Accordingly, the present invention firstly provides the use of polydiene having terminal epoxy groups as oxygen scavenger.